1. Technical Field
The embodiments described herein relate generally to the manufacture of golf balls, and specifically to a cavity mold assembly for injection molding a golf ball cover on a golf ball, using a layer of insulating material between the metal cavity mold halves and the injection molded material to slow the freezing of the injected material and thus enable a thin cover or a low-flow material cover to be molded before “material freeze-off” occurs.
2. Related Art
Some of the most popular balls in the golf industry have polyurethane covers that are less than 0.035″ thick, which is too thin to injection mold easily using standard injection molding cavities. As a result, companies such as Acushnet, Callaway, and Taylor Made often use either a casting or RIM system to apply thin covers to their golf balls. Casting and Reaction Injection Mold (RIM) systems are expensive and very difficult to operate compared to an injection molding system. Injection molded TPU materials are now available that have the toughness of casted or RIM polyurethane; see for example U.S. Pat. No. 7,540,990. However, without the technology to mold thin polyurethane covers, golf ball companies must resort to casting or RIM processes if they want to put a thin polyurethane cover on a golf ball.
Typically golf ball injection molding cavities are made of metal, which is a good conductor of heat. It is difficult to injection mold very thin covers on golf balls using materials such as thermoplastics or thermoplastic elastomers because a point is reached where the heat removal from the injected material by the metal mold is such that the melted material can not fill the mold before “material freezing off” occurs. Even with relatively thick covers, the use of a very low flow material can also have problems with “material freezing off” before the mold can be completely filled.